What happens to computers and laptops taken to UK tips?

I've been to several local tips and seen loads of computers and laptops being thrown away. I was wondering what happens to these and whether I'd be able to ask to take them. Several of the computers I've seen have been like Mac-book Airs, Dell Alienwares and some touch screen all-in-ones. I know they probably are broken but I could put the parts to good use. Do you know if it's allowed or would I have to pay?